1. Field of the Invention
This invention relates to a roof covering sheet material. This invention also relates to a built up roof comprising sheathing over which is disposed a roof covering sheet material disposed away from the sheathing by a spacing means, the spacing means, in accordance with the invention, being in the form of a mat of resilient non-woven wires, threads, or fibers of high air volume.
2. Discussion of the Prior Art
In the covering of roofs or other surfaces in buildings, especially where damp interiors are involved, a roof cover sheet material is used which is provided on its side facing the sheathing with a means for forming an air space. By the air space produced in this manner between the roof cover sheet material and the sheathing the air and vapor pressure can be equalized, thereby preventing the formation of bubbles under the roll roofing or other roof covering material. At the same time, such spacing means permit movement between the roof cover and the sheathing, thereby preventing the cracking of the roof cover when the sheathing moves as a result of thermal expansion or mechanical stress.
Roll roofing material is known in which uniformly sized stone material serves as the spacing means, especially uniformly sized grains of fire expanded clay. These spacing means have the advantage that the roofing can be put up in rolls without the need to dust the side provided with the spacing means to prevent adhesion when it is rolled, or to insert layers or paper for that purpose. These spacing means, however, have the disadvantage that the roofing cannot be made so as to be sealable by heat, and therefore a binding agent must be provided on the surface of the sheathing to hold the material down. Heated bitumen or asphalt is usually used as such binding agent, being applied spot-wise in sufficient amount to fill up the interstices between the spacing means with such binding agents with such "hold-down spots". Then, however, an unyielding bond is produced between the roofing and the sheathing.
Spacing means of metal or of plastic are also known, which are cemented to the roof cover material with hot bitumen. This, however, has the disadvantage that at the points at which the spacing means are cemented to the sheathing, an unyielding joint between the sheathing and the cover material is produced whereby movement between the two is prevented and the air space is interrupted. Another disadvantage is that, in the known embodiments, the spacing means are so rigid that irregularities on the surface of the sheathing, especially when the sheathing has a very rough surface, show in the top of the roof cover material, or they result in an inadequate bond.
Spacing means of plastic are also known, which can be burned away spot-wise so that direct contact between the cover material and the sheathing is produced, so that cementing with a binding agent, such as bitumen or the like, is possible. This again, however, results in an unyielding bond between the cover material and the sheathing which prevents movement, interrupts the air space, and causes irregularities in the sheathing to become manifest on the upper surface of the cover material.